[ET-VK] Remove CopyNode

`CopyNode` simply copies data from one image texture to another image texture of the same size.

During inception of the graph runtime, it was useful to validate that components were working, but won't serve us any use in the future.

Differential Revision: [D54369109](https://our.internmc.facebook.com/intern/diff/D54369109/)

[ghstack-poisoned]

Author: jorgep31415